These all seem very small given that they have no effect when they're on the battlefield. Even Genesis was a 4/4, and Glory was a 3/3 flyer, and they weren't mythic (admittedly mythic didn't exist at the time).

Might I suggest True Conviction for the enchantment effect?

­True Conviction is a great idea.

I don't like it being 6/6 (white shouldn't casually get big creatures outside cycles or special occasions). I prefer it it was itself a 3/3 with double strike and lifelink or something.

Also, the wording is "...and you control three or more Plains,...".

This is a cycle: Saviour, Candour, Odour, Clamour, Splendour.

Sure, but the cycle isn't tight at 6/6 for 6. White should not get creatures so efficient in size only.

Hm. Good point.

Well, it's a callback to Personal Incarnation, which is also CMC6... But the mythic "All my creatures rock your socks now" is a bit ott.

Woah, wait a second... Double Strike and Lifelink starting on round 3, assuming you have a way to pitch a card from your hand? Sorry to be a buzz-kill, but that's waaay too good. The most powerful of the incarnations was a tier 1 card named Wonder. It provided Levitation. That's a full colorless and a colored mana cheaper than True Conviction... and Wonder is already an all-star.

Requiring 3 Plains in play to pick this up isn't much of a drawback, since it's almost guaranteed to happen by round 3... when you attack. Personally, I don't think this card is reasonable unless there's at least 5 Plains in play. Then it would be devastating... but would at least it would sit at the top of a curve.

Note that, assuming this isn't in Standard with shocklands, getting it on T3 requires a mono-white deck, which is quite a restriction; especially once you factor in a way to self-discard as well! There's Patrol Hound, Icatian Crier, and, erm, anything else? That's at all playable?

With a card like this? Refusing to play a land on turn one sound like a viable option. No, really... I'd do that all the time. Other than that, how about Grafted Skullcap, Molten-Tail Masticore, Scroll of Griselbrand, Grimoire of the Dead or Mask of Memory? Or just cast something like Tithe to put your hand count up to 8. That, and you'd have to make sure that there are no cheap artifacts, lands or white cards in this set that allow you to discard cards.

If we assume no dual land types, then we would be forced to add blue or black to the deck to get a wider selection. May I suggest using a signet or something like Chromatic Sphere to get there? Racing 5 Plains out is hard to do... but sneaking an artifact onto the table that gets us colored mana by round 3 isn't very hard.